Direction-finding makes it possible to determine the direction of a source of radiation. Conventional applications are manual direction-finding and automatic direction-finding.
Automatic direction-finding is largely used on fixed installations or on mobile ones (aeroplanes, boat, vehicle). The indication of direction is available in the form of a bearing (angle between the wearer and the apparent direction) or an indication of deviation of right/left type.
Manual direction-finding is often used for seeking the source of emission with the aid of an antenna or a sensor oriented by hand. This type of direction-finder rests on the search for minimum or maximum reception without delivering the information of relative position of the direction of the source with respect to the scanning sensor or antenna.
The two types of direction-finding require the reading of an instrument often associated with listening in on a receiver or loud-speaker to allow the source to be identified. Manual direction-finding does not allow a free-hand search of the source of radiation.
As described in U.S. Pat. No. 5,068,832, a personal direction-finding apparatus for detecting an ultrasound radiation and locating the direction of the source emitting this radiation, is already known. This apparatus comprises a local oscillator for converting the inaudible frequencies of the ultrasound signal into frequencies included in the range of audible sounds.
U.S. Pat. No. 4,774,515 discloses an apparatus for indicating normal attitude to give an indication of a normal attitude to an individual jointly with a means for producing a signal representing the attitude in real time of the indiviual in space and a means for placing, in three-dimensional space, the normal indication relative to the individual in response to the signal in real time representing the attitude in real time, so as to give the individual a normal indication relative to the attitude in real time of the individual in space.